Hydraulic pump with a built-in electric motor

ABSTRACT

A hydraulic pump with a built-in electric motor wherein an electric motor and a pump unit are arranged in tandem fashion and accommodated within a common housing. In this pump, the housing is in the form of a metal box having a rectangular parallelepiped external shape and forms an electric motor frame fixedly accommodating a stator of the electric motor therein. A space in the metal box on the electric motor side is separated as a dry space from an internal space of said pump unit by a seal mechanism. At least one hydraulic oil receiving chamber is formed in a peripheral wall of the metal box, and the hydraulic oil receiving chamber is communicated with a passage for receiving return oil externally and another passage communicating with a suction port of the pump unit. The pump is capable of simultaneously achieving the cooling of a built-in electric motor and the prevention of contamination of hydraulic oil due to the rotation of the electric motor, without any possibility of electrical troubles with the built-in electric motor even if a water-containing hydraulic oil or aqueous hydraulic oil is fed and discharged.

This application is a U.S. National Phase Application under 35 USC 371of International Application PCT/JP00/02631 (not published in English)filed Apr. 21, 2000.

FIELD OF THE INVENTION

The present invention relates to a hydraulic pump with a built-inelectric motor in which an electric motor and a pump unit that aredisposed in tandem along the axis of rotation are received in a commonhousing.

BACKGROUND OF THE INVENTION

As disclosed, for example, in JP-A-0988807, a hydraulic pump with abuilt-in electric motor of the type in which an oil-immersed electricmotor and a hydraulic pump unit are disposed in tandem along the axis ofrotation and interconnected by a common shaft whereby a drain oildischarged from the hydraulic pump unit within a common housing isintroduced into and discharged to the outside of the oil-immersedelectric motor to thereby cool the electric motor with the pump drainoil, has been known in the art.

Although the hydraulic pump with a built-in electric motor of the typein which the built-in electric motor is immersed and cooled with thedrain oil from the pump unit is excellent in cooling efficiency due tothe fact that structurally the electric motor coils which are subject tocooling is in direct contact with the hydraulic oil or the coolingmedium, in the case where water is introduced into the hydraulic oil orthe hydraulic oil itself is an aqueous hydraulic oil, difficulties areencountered in that not only there is the danger of causing such troubleas an electric short-circuiting inside the electric motor, but also veryfine metal foreign particles produced within the rotating electric motortend to enter the hydraulic oil thus making a filter treatmentunavoidable for the recirculation of the drain oil and requiringadditional time and labor for the maintenance of the hydraulic systemincluding a frequent changing of filters, etc.

Further, in the conventional hydraulic pump with a built-in electricmotor, the electric motor-is of the oil immersed construction and itsinstallation posture is permanently fixed so that not only there is alimitation to the installation place within machinery which utilize suchpump, but also a piping connection to the hydraulic oil reservoir tankis required thus making it necessary to suffer a certain degree ofcomplication in the construction of the installation portion.

SUMMARY OF THE INVENTION

In view of the foregoing deficiencies in the prior art, it is theprimary object of the present invention to provide a hydraulic pump witha built-in electric motor capable of not only simultaneously achievingthe cooling of a built-in electric motor and the prevention ofcontamination of a hydraulic oil due to the rotation of the electricmotor, but also preventing the occurrence of electrical troubles withthe built-in electric motor even if a water-containing hydraulic oil oraqueous hydraulic oil is fed and discharged. Also, it is another objectof the present invention to increase the degree of freedom of design forselecting the installation positions or to make it possible to eliminatethe need for piping connection to a reservoir tank.

In accordance with the present invention, there is thus provided ahydraulic pump with a built-in electric motor in which an electric motorand a pump unit are arranged in tandem fashion and accommodated within acommon housing. More particularly, the housing is in the form of a metalbox having a rectangular parallelepiped external shape and forms anelectric motor frame fixedly accommodating a stator of said electricmotor therein. A space in the metal box on the electric motor side isseparated as a dry or atmospheric space from the internal space of thepump unit by a seal mechanism. At least one hydraulic oil receivingchamber is formed in the peripheral wall of the metal box, and that thehydraulic oil receiving chamber is communicated with a passage forreceiving a return oil from the outside and a passage leading to thesuction port of the pump unit.

Here, the so-called seal mechanism of the present invention means allkinds of oil leakage seal mechanisms capable of transmission ofrotation, e.g., those which smoothly transmit the rotation of theelectric motor to the rotor of the pump unit and prevent the leakage ofthe oil from the internal space of the pump unit to the space on theelectric motor side. As regards specific examples of such sealmechanism, where the rotary shaft of the electric motor and the pumpunit is composed of a single common shaft, for example, it is possibleto cite an annular oil seal disposed adjacent to a bearing in a pumpunit case between the electric motor and the pump unit, oralternatively, where the rotary shaft of the electric motor and therotor rotating shaft of the pump unit are disconnected separate shafts,it is possible to cite a magnetic coupling with an oil leakproof seal sodesigned that magnets are disposed on the inner peripheral surface of acoupling socket provided on the forward end of the rotary shaft of theelectric motor, that corresponding magnets are also disposed on the endof the rotor rotating shaft of the pump unit that is inserted in thesocket through a diametrical gap, that the end of the rotor rotatingshaft is covered with a seal cap through an annular gap between themagnets and that the opening flange of the seal cap is sealingly fixedto the case side of the pump unit.

In the hydraulic oil pump with a built-in electric motor according tothe present invention, the housing forms the electric motor portion andalso the electric motor portion within the housing is disposed in thedry space separated from the internal space of the pump unit by the sealmechanism whereby the hydraulic oil sucked into the pump unit flowsthrough the hydraulic oil receiving chamber disposed in the housingperipheral wall separately from the dry space and it does not contactwith the rotating parts of the electric motor; thus, there is no dangerof the hydraulic oil being contaminated with metal foreign particlesemitted from the rotating electric motor and also there is no danger ofelectrical troubles being caused within the electrical motor due to thehydraulic oil even if the hydraulic oil contains water or the hydraulicoil itself is an aqueous hydraulic operational fluid. Moreover, in thehydraulic pump with a built-in electric motor according to theinvention, the housing itself forms a liquid-cooling jacket for coolingthe electric motor and therefore the cooling of the electric motor isattained effectively. While, in this case, the generation of heat fromthe electric motor is caused mainly by the windings of its stator, thestator is attached to the metal box forming the housing and thus theheat generated from the stator windings is directly transmitted to themetal box by heat conduction, thereby ensuring an effective coolingowing to not only the heat dissipation effect of the outer surface ofthe metal box itself but also the fact that the heat is absorbed throughheat conduction by the hydraulic oil in the hydraulic oil receivingchamber through the metal box.

The pump unit is driven by the rotation of the electric motor so thatthe hydraulic oil sucked from the hydraulic oil receiving chamber isdischarged as a pressurized oil and this-pressurized oil is returned asreturn oil to the hydraulic oil receiving chamber after it has performeda work in an external load actuator connected to the pump. Preferably,the drain oil from the pump unit is also introduced into the hydraulicoil receiving chamber so that although the amount of the drain oil isvery small as compared with the return oil, it is sufficient to alwayscause a flow of the hydraulic oil in the hydraulic oil receiving chamberduring the operation of the pump and therefore it is effective not onlyin cooling the electric motor the flow of the hydraulic oil in thehydraulic oil receiving chamber but also in raising the temperature ofthe hydraulic oil during the warming-up operation in the cold time suchas the winter season.

In order to perform the cooling of the electric motor more effectively,it is effective to add a fan radiator which utilizes the rotation of theelectric motor. In this case, the fan radiator is mounted to lie alongthe end plate of the housing (the metal box) on the electric motor sideand the fan radiator is rotated by directly connecting it to the end ofthe rotary shaft of the electric motor. The return oil and the drain oilflowing into the hydraulic oil receiving chamber are passed through theradiator so that the hydraulic oil within the radiator is air-cooledfrom the outside of the metal box by an air stream caused by the fan.Note that in this case, it is preferable to add a suitable air streamdeflecting structure such as a hood to the fan radiator so that the airstream by the fan flows along the housing surface and it is alsopreferable to further additionally form heat dissipation fins or groovesin the housing outer surface so as to increase the surface area.

In the hydraulic pump with a built-in electric motor according to thepresent invention, the housing in the form of the electric motor framehaving the electric motor stator internally attached thereto is composedof the metal box of the rectangular parallelepiped external shape sothat in the section perpendicular to its axis of rotation, there arefour areas of substantially triangular shape at the four corners,respectively, between the external contour of substantially rectangularparallelepiped, preferably square shape and the internal circular spacefor disposing the electric motor and the pump unit therein and thereforethese areas can be utilized for the formation of hydraulic oil receivingchambers.

For instance, assuming that the external dimensions of the squaresection of the metal box are about 280 mm*280 mm, the inner diameter ofthe internal space for disposing the electric motor, etc., therein isabout 160 mm and the axial length is about 280 mm, the hydraulic oilreceiving chambers constituted by the four spaces of substantiallytriangular sectional shape formed in conformity to the four corner inthe peripheral wall of the metal box can be utilized as a reservoirhaving an inner volume of about 10 liters in total. In the event that areservoir of a greater volume is required, it is possible to increasethe volume by mounting an auxiliary tank to lie on the housing byutilizing the fact that the housing is of the rectangular parallelepipedexternal shape.

In the hydraulic pump with a built-in electric motor according to thepresent invention, the housing is rectangular parallelepiped in externalshape so that the pump can be installed by selecting either of verticaland horizontal arrangements each selectively using one or the other ofthe adjoining two sides of the housing as its top surface and theinstallation posture corresponding to the installation space can beselected. In this case, preferably an opening capable of selectively anddetachably mounting therein an air breather and an oil level measuringwindow is formed in each of the two sides so that as for example, theair breather is mounted in the opening formed in one of the sidesserving as the top surface and the oil level measuring window isattached to the opening in the other side in the case of the verticalarrangement, whereas in the case of the horizontal arrangement themounting of the air breather and the oil level measuring window isreversed with each other. Similarly, when mounting an auxiliary tank,one of these openings is used for communicating the tank with thehydraulic oil receiving chamber and the tank is formed with openingseach for selectively mounting the air breather and the oil levelmeasuring window therein in place of the opening used for suchcommunicating purposes.

The foregoing and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription of its embodiments made with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory diagram which is partly cut away to show, asviewed from the side, the principal construction of a hydraulic pumpwith a built-in electric motor according to a first embodiment of thepresent invention;

FIG. 2 is a half-cut explanatory diagram showing, as viewed from theback, the right-side half of the housing of the hydraulic pump with abuilt-in electric motor shown in FIG. 1;

FIG. 3 is a front view showing the external appearance of the hydraulicpump with a built-in electric motor according to the first embodiment;

FIG. 4 is a left side view showing the external appearance of thehydraulic pump with a built-in electric motor according to the firstembodiment;

FIG. 5 is a rear view showing the external appearance of the hydraulicpump with a built-in electric motor according to the first embodiment;

FIG. 6 is a plan view showing the external appearance of the hydraulicpump with a built-in electric motor according to the first embodiment;

FIG. 7 is a left side view of a hydraulic pump with a built-in electricmotor according to a modified embodiment additionally including a fanradiator;

FIG. 8 is a circuit diagram showing the construction of the modifiedembodiment by means of graphical hydraulic circuit symbols;

FIG. 9 is a side view showing an example of a vertically arranged pumpwith the addition of an auxiliary tank;

FIG. 10 is a front view of the vertically arranged pump with theaddition of an auxiliary tank;

FIG. 11 is a front view of the horizontally arranged pump with theaddition of an auxiliary tank; and

FIG. 12 is a principal sectional view of another modified embodimentshowing another exemplary seal mechanism.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIGS. 1 to 6, in a hydraulic pump with a built-in electricmotor according to a preferred embodiment of the present invention, ahousing is formed by a casted metal box 1 having a substantially squareshaped external contour in cross section and end covers 2 and 3 so thata rotor 5 of an electric motor and a rotor 6 of a pump unit are fixedlyarranged in tandem fashion along a single-shaft common rotary shaft 4which is rotatably supported by the end covers within the housing, and astator 7 of the electric motor is directly attached to the inner surfaceof the metal box 1 at the position corresponding to the rotor 5; also,the rotor 6 is enclosed by a case 8 of the pump unit which is attachedto the front-side end cover 2 so as to be received within the housingthereby accommodating the electric motor and the pump unit within thecommon housing.

The metal box 1 is a box member having a cubic external shape with itsinterior forming a cylindrical space, thus forming the peripheral wallof the housing as an electric motor frame having the electric motorstator 7 attached to its inner surface. The electric motor-side space inthe metal box 1 is an atmospheric space separated from the space in thecase 8 of the pump unit by an oil seal 9 which is an example of a sealmechanism mounted on the rotary shaft 4 in the tail end portion of thepump unit case 8.

As shown in FIG. 2, four hydraulic oil receiving chambers 10 a to 10 dare in the peripheral wall of the metal box 1, and connected to thehydraulic oil receiving chambers are passages for receiving a return oilfrom the outside through the end cover 2 and passages leading to thesuction port and the drain port of the pump unit. In the meal box 1forming the housing of the hydraulic pump with a built-in electric motoraccording to the present embodiment, as viewed in the cross sectionperpendicular to the rotary shaft 4, there are four areas ofsubstantially triangular shape at the four corners between the externalcontour of substantially square shape and the internal cylindricalspace, and these area are utilized as the areas for forming thehydraulic oil receiving chambers 10 a to 10 d.

Note that in the present embodiment the external dimensions of thesquare section of the metal box 1 are about 280 mm×280 mm, the innerdiameter and axial length of its internal cylindrical space arerespectively about 160 mm and about 280 mm, and the four hydraulic oilreceiving chambers 10 a to 10 d having substantially triangularsectional shape and formed at the four corners in the peripheral wall ofthe metal box 1 can be utilized as a reservoir having an inner volume ofabout 10 liters in total.

The end cover 2 on the housing front side is a pump cover fastened tothe pump case 8 by flange joining with bolts and, as shown in FIG. 6,this pump cover is provided with a tank port 11 (on the left side asviewed from the front), a drain port 12 (similarly on the right side) onthe housing top surface side and a discharge port 13 (FIG. 3) on thehousing front side for external connection purposes. The tank port 11and the internal drain port are communicated with the hydraulic oilreceiving chamber 10 b on the top left side, and the suction port of thepump unit is communicated with the hydraulic oil receiving chamber 10 aon the top right side. Also, arranged on the front side of the pumpcover 2 are a delivery rate adjusting screw 14, a pressure regulatingscrew 15 and a pressure gauge 16 for the pump unit with the gauge 16having its display face turned upward. It is to be noted that mountedabout the center of the housing left side face is a terminal block case17 for the electric wirings provided mainly for the electric motor.

The end cover 2 is provided with internal passages (not shown) forrespectively connecting the upper and lower hydraulic oil receivingchambers 10 b, 10 c and 10 a, 10 d of the metal box 1 on the left andright sides, whereas the end cover 3 on the housing back side isprovided with an internal passage for internally connecting the lowerleft and right hydraulic oil receiving chambers 10 c and 10 d of themetal box 1 with each other. By virtue of the connection of therespective hydraulic oil receiving chambers by the internal passages ofthe end covers 2 and 3, a continuous path is formed so that the returnoil directed to the tank port 11 from the outside and the internal drainoil of the pump unit are sequentially passed through the respectivehydraulic oil receiving chambers so as to reach the suction port of thepump unit. In the illustrated embodiment, this path is in the order ofthe hydraulic i receiving chambers 10 b, 10 c, 10 d and 10 a.

As will be best seen from FIG. 4, an opening concurrently serving as anoil filling port is formed in the housing top so as to communicate withthe hydraulic oil receiving chamber 10 a through the peripheral wall ofthe housing and an air breather 18 is removably mounted in this openingin the illustrated condition. Similarly, another opening concurrentlyserving as an oil filling port is also formed in the left side face ofthe housing at the position corresponding to the previous opening so asto communicate with the hydraulic oil receiving chamber 10 b through thehousing peripheral wall, and an oil level measuring window 19 isremovably mounted in this opening in the illustrated condition. Theseopenings respectively formed in the housing top and left side face areconcurrent openings in which the air breather 18 and the oil levelmeasuring window 19 can be changeably mounted, and also the housing topopening having the air breather 18 mounted therein in the illustratedcondition can be used as a through hole which provides a communicationbetween an auxiliary tank (20: FIGS. 10 and 11) and the hydraulic oilreceiving chamber 10 a when the auxiliary tank is additionally installedas will be described later.

In the hydraulic pump with a built-in electric motor according to thepresent embodiment, the housing constitutes the electric motor frame andthe electric motor portion within the housing is in the dry spaceseparated from the internal space of the pump unit by the oil seal 9,with the result that the return oil arriving the tank port 11 and thedrain oil flow by passing sequentially through the respective hydraulicoil receiving chambers arranged in the housing peripheral wallindependently of the dry space and are sucked into the suction port ofthe pump unit, thereby causing the housing itself to serve as aliquid-cooling jacket for cooling the electric motor. While the heatgeneration of the electric motor is mainly produced from the windings ofthe stator 7, the stator is attached to the inner surface of the metalbox 1 forming the housing so that the heat generated from the statorwindings is directly transmitted by heat conduction to the metal box 1and the generated heat is absorbed by heat conduction by the hydraulicoil in the respective hydraulic oil receiving chambers through the metalbox 1 in addition to the heat dissipation effect of the outer surface ofthe metal box itself, thereby making it possible to effectively cool theelectric motor. Also, in this case, the hydraulic oil does not contactwith the rotating parts of the electric motor so that there is no dangerof the hydraulic oil being contaminated with metal foreign particlesproduced from the rotating electric motor and also there is no danger ofcausing any electric trouble e.g., a short-circuiting in the electricmotor even in the case where the hydraulic oil contains water or thehydraulic oil itself is an aqueous hydraulic oil.

When the rotor 6 of the pump unit is driven by the rotation of the rotor5 of the electric motor, the pump unit discharges the hydraulic oilsucked from the hydraulic oil receiving chambers as a pressurized oilfrom the discharge port 13 and the pressurized oil is returned as areturn oil to the hydraulic oil receiving chambers through the tank port11 after it has performed a work in an external load actuator (notshown) connected to the pump. The drain oil from the pump unit is alsointroduced into the hydraulic oil receiving chambers so that althoughthe amount of the drain oil is very small as compared with the returnoil, it is sufficient to always cause a flow of the hydraulic oil in thehydraulic oil receiving chambers during the operation of the pump andtherefore not only the cooling of the electric motor by the flow of thehydraulic oil in the hydraulic oil receiving chambers is made effectivebut also it is effective raising the oil temperature of the hydraulicoil during, for example, the warming-up operation a cold time such asthe winter season.

While a plurality of fins or grooves 21 are formed in the left and rightside faces of the metal box 1 constituting the housing outer peripheralsurface so as to increase the heat dissipation area, a fan radiator 22utilizing the rotation of the electric motor can be added as shown inFIG. 7 so as to perform the cooling of the electric motor moreeffectively. In this case, it is only necessary to replace themotor-side end plate 3 of the housing (the metal box) with a radiatormounting end plate 23 of a special specification and the fan radiator 22is assembled to lie along the end plate 23 so as to rotate a fan 24 ofthe radiator by directly connecting it to the end of the rotary shaft 4of the electric motor by a socket joint system, for example. The endplate 23 contains therein passages for communication between therespective hydraulic oil receiving chambers and the interior of theradiator so that the interconnection between the left and righthydraulic oil receiving chambers 10 a, 10 b and 10 c, 10 d,respectively, are effected within the radiator in place of the end plate3. The return oil and the drain oil flowing into the hydraulic oilreceiving chambers pass through the interior of the radiator so that thehydraulic oil within the radiator is air-cooled by an air stream causedby the fan 24. A hood 25 is also mounted on the fan radiator so as todeflect the generated air stream to flow along the housing outerperipheral surface from the back side to the front side and this makes amore effective cooling possible. The construction of this modifiedembodiment is as shown by the hydraulic circuit diagram of FIG. 8 andthe corresponding component elements are designated by the samereference numerals.

As mentioned previously, in the present embodiment the metal box 1itself forms the hydraulic oil receiving chambers of about 10 liters involume; however, in the event that a reservoir of a greater volume isrequired in the pump utilizing the same housing, the fact that theexternal shape of the housing is rectangular parallelepiped is utilizedso that an auxiliary tank 20 is mounted by placing it on the housing asshown in FIGS. 9 to 11 to increase the volume of the reservoir. Formedin the top of the auxiliary tank 20 are openings of the samespecifications as the openings respectively formed in the top and leftside faces of the metal box 1 so as to concurrently serve as oil fillingports and selectively mount therein the air breather 18 and the oillevel measuring window 19, and also formed through the bottom surface ofthe auxiliary tank is an opening which is connected with the opening inthe top of the metal box 1 to form a communicating opening when theauxiliary tank is placed on the top of the metal box 1.

FIGS. 9 and 10 show an example of a vertically arranged posture in whichthe hydraulic pump shown in FIGS. 1 to 6 is used in its posture as suchand the auxiliary tank 20 is arranged to lie on the top of the metal box1; thus, the auxiliary tank 20 is communicated with the interior of thehydraulic oil receiving chamber 10 a through the opening in the top ofthe metal box 1 from which the air breather 18 has been removed and theair breather 18 which had been on the top of the metal box 1 is nowmounted in the similar opening (serving concurrently as an oil fillingport) in the top of the auxiliary tank 20. In the case of the presentembodiment, the auxiliary tank 20 has a volume of about 10 litersthereby realizing a reservoir volume of about 20 liters in total.

In the hydraulic pump with a built-in electric motor according to thepresent invention,its housing has a rectangular parallelepiped externalshape so that it is possible to install the pump by selectively using avertically installed arrangement and a horizontally installedarrangement each of which selectively utilizes as its top one or theother of the adjoining two sides of the housing and the desiredinstallation posture can be selected in conformity with the installationspace. Of these arrangements, an example of the vertically installedarrangement is as shown in FIGS. 9 and 10, and an example of thehorizontally installed arrangement is as shown in FIG. 11.

In the case of the horizontally installed arrangement, the end plates 2and 3 (or the end plate 23) are left in their positions as such and themetal box 1 alone is tilted 90 degrees about the rotary shaft 4 torearrange such that the previous top is now the right side face and theprevious left side face is now the top. Thus, the opening having the airbreather 18 mounted therein in FIGS. 1 to 6 is now the opening forconnection with the auxiliary tank 20 and the air breather 18 is mountedin the opening having previously mounted therein the oil level measuringwindow 19 (the opening concurrently serving as the oil filling port);also, the oil level measuring window 19 is mounted in the top opening ofthe auxiliary tank 20 in which the air breather is mounted in the caseof the vertically installed arrangement.

FIG. 12 shows another example of the seal mechanism. This modifiedembodiment uses a separate shaft construction in which a rotary shaft 4a of an electric motor and a rotor rotating shaft 4 b of a pump unit areseparated from each other, and attached to the forward end of theelectric motor rotary shaft 4 a is a coupling socket 26 having attachedto the inner peripheral surface thereof a plurality of circumferentiallysplit magnet pieces 27 a.

An external bearing 28 rotatably supports the forward end of thecoupling socket 26 at the end of a pump case 8 and an internal bearing29 rotatably supports the rotor rotating shaft 4 b. The rotor rotatingshaft 4 b of the pump unit is inserted in the socket 26 through adiametrical gap and attached to the end of the shaft 4 b are a pluralityof magnet pieces 27 b which correspond to but differ in number from themagnet pieces 27 a. The magnet pieces 27 a and 27 b constitute amagnetic coupling which transmits a rotary torque by magnetic attractiveforce between the magnet pieces 27 a and 27 b through an annular gap sothat the rotor rotating shaft 4 b of the pump unit is driven intorotation by the rotary shaft 4 a of the electric motor.

The end of the rotor rotating shaft 4 b projects to the outside of thepump case 8 and its outer side is covered in an oil-tight manner by aseal cap 30. The seal cap 30 is made from a nonmagnetic material such asstainless steel, copper alloy or plastic material which is formed into abottomed cylindrical shape with an externally extended flange portion atits opening edge and it has a thickness which seals against the leakageof the oil with a sufficient mechanical strength without any loss of themagnetic attractive force between the magnet pieces 27 a and 27 b. Theopening edge of the seal cap 30 is sealingly attached to the end face ofthe pump case 8 so that the seal cap 30 is a nonrotating part with itsperipheral wall portion positioned in the annular gap between the magnetpieces 27 a and 27 b, and the external and internal magnet pieces 27 aand 27 b are in a relatively rotatable relation with each other.

It is to be noted that the foregoing embodiments and modifications areonly for the purpose of showing some typical embodiments of the presentinvention and it should be understood that any other modifications whichare obvious to those skilled in the art belong to the technical scope ofthe present invention. For instance, it is of course possible to makesuch modifications including one in which a return filter unit 32 ismounted on the side face of the metal box 1 as shown in FIGS. 9 to 11,another in which various oil pressure control valve, pressure regulatingvalve, selector valve, manifolds, etc., are stacked up and arranged onthe outer surface of the pump cover by utilizing the fact that the pumpunit is collectively arranged on the end cover 2 side, and still anotherin which a delivery rate sensor required for electrically controllingthe hydraulic pump, such as, a potentiometer for detecting the tiltangle of a swash plate in the case of the pump unit composed of an axialpiston pump assembly, a pressure sensor for producing an electric signalindicative of the delivery pressure or the like is incorporated in thepump cover.

As described hereinabove, by virtue of the fact that in the hydraulicpump with a built-in electric motor according to the present inventionthe housing forms the electric motor frame, that the electric motorportion in the housing is in the dry space separated from the internalspace of the pump unit by the seal mechanism and that the hydraulic oilsucked into the pump unit flows through the hydraulic oil receivingchambers arranged in the housing peripheral wall independently of thedry space and so it does not contact with the rotating parts of theelectric motor,there is no danger of any metal foreign particlesproduced by the rotating electric motor entering the hydraulic oil andalso there is no danger of electric troubles being caused within theelectric motor due to the hydraulic oil containing water or an aqueoushydraulic oil constituting the hydraulic oil itself. Moreover, thehousing itself forms a liquid-cooling jacket for cooling the elect motorwith the result that the heat generated from the electric motor isabsorbed through heat conduction by the hydraulic oil in the hydraulicoil receiving chambers through the metal box in addition to the heatdissipation effect of the outer surface of the metal box itself andtherefore the electric motor can be effectively cooled by this factcoupled with the flowing of the hydraulic oil in the hydraulic oilreceiving chambers.

In addition, a fan radiator utilizing the rotation of the electric motorcan be added so as to cool the electric motor more effectively, and alsoa still increased cooling effect can be attained by causing the returnoil and the drain oil flowing into the hydraulic oil receiving chambersto pass through the radiator so as to air-cool the hydraulic oil in theradiator from the outside of the metal box by an air stream caused bythe fan.

Further, in the hydraulic pump with a built-in electric motor accordingto the present invention the housing in the form of the electric motorframe having the electric motor stator internally attached thereto iscomposed of the metal box of the rectangular parallelepiped externalshape so that in the section perpendicular to its axis of rotation,there are four areas of substantially triangular shape at the fourcorners between the external contour of substantially rectangularparallelepiped shape, preferably square shape and the circular space fordisposing the electric motor and the pump unit therein and thus theseareas can be used for its hydraulic oil receiving chambers so as toprovide a hydraulic pump with a built-in electric motor having a compactexternal shape and including a reservoir; moreover, where a reservoir ofa greater volume is required, it is possible to increase the volume bymounting an auxiliary tank so as to lie on the housing by utilizing thefact that the external shape of the housing is rectangularparallelepiped, and in this case there is also the advantage that theinstallation can be effected by making a selection between ahorizontally installed arrangement and a vertically installedarrangement each utilizing one or the other of the adjoining two facesof the housing of the rectangular parallelepiped external shape as itstop face, and the installation posture can be selected in accordancewith the installation space.

What is claimed is:
 1. A hydraulic pump comprising: an electric motorand a pump unit arranged in tandem fashion and accommodated within acommon housing, wherein said housing is in the form of a metal boxhaving a rectangular parallelepiped external shape and forms an electricmotor frame fixedly accommodating a stator of said electric motortherein, wherein a space in said metal box on said electric motor sideis separated as a dry space from an internal space of said pump unit bya seal mechanism, wherein at least one hydraulic oil receiving chamberis formed in a peripheral wall of said metal box, wherein said hydraulicoil receiving chamber is communicated with a passage for receivingreturn oil externally and another passage communicating with a suctionport of said pump unit, and wherein a fan radiator including a fancoupled to a rotary shaft of said electric motor is attached to one endcover of said housing which is on a side of said electric motor wherebythe return oil and drain oil flowing into said hydraulic oil receivingchamber are passed through said fan radiator so as to air-cool thehydraulic oil within said radiator from outside of said metal box by anair stream caused by said fan.
 2. A hydraulic pump comprising: anelectric motor and a pump unit arranged in tandem fashion andaccommodated within a common housing, wherein said housing is in theform of a metal box having a rectangular parallelepiped external shapeand forms an electric motor frame fixedly accommodating a stator of saidelectric motor therein, wherein a space in said metal box on saidelectric motor side is separated as a dry space from an internal spaceof said pump unit by a seal mechanism, wherein at least one hydraulicoil receiving chamber is formed in a peripheral wall of said metal box,wherein said hydraulic oil receiving chamber is communicated with apassage for receiving return oil externally and another passagecommunicating with a suction port of said pump unit, and wherein aplurality of hydraulic oil receiving chambers are constituted by fourspaces of substantially triangular sectional shape formed incorrespondence to four corners in the peripheral wall of said metal box.3. A hydraulic pump with a built-in electric motor as set forth in claim1, wherein a plurality of hydraulic oil receiving chambers areconstituted by four spaces of substantially triangular sectional shapeformed in correspondence to four corners in the peripheral wall of saidmetal box.
 4. A hydraulic pump with a built-in electric motor as setforth in claim 1, wherein an auxiliary tank for communicating with-saidhydraulic oil receiving chamber is additional mounted so as to be placedon said housing.
 5. A hydraulic pump with a built-in electric motor asset forth in claim 2, wherein an auxiliary tank for communicating withsaid hydraulic oil receiving chambers is additionally mounted so as tobe placed on said housing.